The present invention relates to a method of distinguishing the front and back surfaces of a processed photographic film.
Processed reversal films (referred to in this specification as films for simplicity) are mounted in cardboard mountings or plastic mountings for use as slides. Commercial laboratories usually return processed slides in cardboard or plastic mountings. It rarely happens in commercial laboratories that the films are mounted in the wrong way.
However, customers sometimes choose to mount films themselves in cardboard or plastic mountings. When this is done, it sometimes happens that films are mounted the wrong way, namely backward.
On occasion, it is necessary to make prints from slides. When making prints from slides mounted backward, the finished prints will show pictures with the right side on the left, namely mirror images.
All of the slide bordered by the mounting must be suitable for projection, and so one must avoid marking either the front or the back surface of the mounted film. As a method of distinguishing the front and/or back surface of film, it is known in the art to measure the difference in reflectance btween the front and back surfaces of a film. This method is based on the fact that the front and back surfaces of film exhibit a difference in reflectivity when wetted with water. For measuring reflectivity by this method, it is required to spray water vapor in the form of steam on both surfaces of the film so that the film will be misted with water.
In this method, however, there is the problem that, since the slides must be wetted well with water for measurement and dried well before printing, a great deal of time is thus spent before printing. Another problem of measurement by this method is that, since the mounting of the slide is unavoidably wetted with steam, the mounting, if it is a cardboard one, is in danger of being torn during the handling of the same. If a slide is held between two transparent glass plates, the slide cannot be subjected to this method.